Multiphase reactors types

Multiphase reactor types are highly varied. The simplest approach to analyzing and predicting their behavior is to focus on the rate limiting steps or segment the reactor and model each segment and its contributions separately. Correlations are invariably a function of phase-based Reynolds and Froude numbers. Fractional volumes and properties of the solids are factors. Where interfacial tension is an important factor, the Weber number can be added. 

MULTIPHASE REACTORS TYPES AND CRITERIA FOR SELECTION FOR A GIVEN APPLICATION... 

Differentiate various multiphase reactor types such as mechanically agitated slurry reactors (MASRs), bubble column slurry reactors (BCSRs), loop slurry reactors (LSRs), and trickle bed reactors (TBRs). 

Early ia the development of chemical reaction engineering, reactants and products were treated as existing ia single homogeneous phases or several discrete phases. The technology has evolved iato viewing reactants and products as residing ia interdependent environments, a most important factor for multiphase reactors which are the most common types encountered. 

Reactor type Triple-feed continuous multiphase chip reactor system Micro-channel width depth length Not given in [28]... 

Reactor type Multiphase packed-bed reactor Gasket material Viton... 

The trickle-bed reactor (TBR) and slurry reactor (SR) are the most commonly used for multiphase reactions in the chemical industries. A new reactor type, the monolithic reactor (MR), offers many advantages. Therefore, these three types of reactors are discussed below in more detail. Their general characteristics are given in Table 5.4-44. With respect to slurry reactors, the focus will be on mechanically agitated slurry reactors (MASR) because these are more widely used in fine chemicals manufacture than column slurry reactors. 

Chemical Kinetics, Tank and Tubular Reactor Fundamentals, Residence Time Distributions, Multiphase Reaction Systems, Basic Reactor Types, Batch Reactor Dynamics, Semi-batch Reactors, Control and Stability of Nonisotheimal Reactors. Complex Reactions with Feeding Strategies, Liquid Phase Tubular Reactors, Gas Phase Tubular Reactors, Axial Dispersion, Unsteady State Tubular Reactor Models... 

We will develop the rest of this chapter assuming that the catalyst is in a sohd phase with the reactants and products in a gas or liquid phase. In Chapter 12 we will consider some of the more complex reactor types, called multiphase reactors, where each phase has a specific residence time. Examples are the riser reactor, the moving bed reactor, and the transport bed reactor. 

We finally arrive at the type of reactor usually encountered in industrial practice the multiphase reactor. Obviously, a reactor has multiple phases whenever its contents do not form a single-phase solution. For two phases these may be gas-liquid, liquid-liquid, gas-solid, and liquid-solid. Listed in Table 12-1 are the names of some of the common important multiple-phase reactors. 

We have encountered many of these reactor types in previous chapters. In Chapter 2 all the reactors in the petroleum refinery were seen to be multiphase, and we will close this chapter by returning to the reactors of the petroleum refinery to see if we can now understand how they operate in a bit more detail. 

Before we deal with these situations, it is instructive to consider a fixed-area version of a membraneless reactor, the falling film reactor. We cannot think of many applications of this reactor type because one usually benefits considerably by using configurations where the surface area is as large as possible, but the falling film reactor leads naturally to the description of many variable-area multiphase reactors. 

Figure 12-7 Sketches of four types of gas-liquid multiphase reactors.

The book starts with a review of kinetics and the batch reactor in Chapter 2, and the material becomes progressively more complex until Chapter 12, which describes all the types of multiphase reactors we can think of This is the standard, linear, boring progression followed in essentially all textbooks. 

Behr A, Beckmann T, Nachtrodt H (2009) Multiphase telomerisation of butadiene with phenol optimisation and scale-up in different reactor types. Dalton Trans 6214—6219... 

Multiphase reactor configurations are strongly influenced by mass transfer operations. Any of the reactor types presented above can be operated as multiphase reactors. 

Knowledge of these types of reactors is important because some industrial reactors approach the idealized types or may be simulated by a number of ideal reactors. In this chapter, we will review the above reactors and their applications in the chemical process industries. Additionally, multiphase reactors such as the fixed and fluidized beds are reviewed. In Chapter 5, the numerical method of analysis will be used to model the concentration-time profiles of various reactions in a batch reactor, and provide sizing of the batch, semi-batch, continuous flow stirred tank, and plug flow reactors for both isothermal and adiabatic conditions. 

Classification by Phase Despite the generic classification by operating mode, reactors are designed to accommodate the reactant phases and provide optimal conditions for reaction. Reactants may be fluid(s) or solid(s), and as such, several reactor types have been developed. Singlephase reactors are typically gas- (or plasma- ) or liquid-phase reactors. Two-phase reactors may be gas-liquid, liquid-liquid, gas-solid, or liquid-solid reactors. Multiphase reactors typically have more than two phases present. The most common type of multiphase reactor is a gas-liquid-solid reactor however, liquid-liquid-solid reactors are also used. The classification by phases will be used to develop the contents of this section. 

FIG. 19-31 Some examples of bubble column reactor types, (a) Conventional bubble column with no internals. (6) Tray bubble column, (c) Packed bubble column with the packing being either an inert or a catalyst. [From Mills, Ramachandran, and Chaudhari, Multiphase Reaction Engineeringfor Fine Chemicals and Pharmaceuticals, Reviews in Chemical Engineering, 8(1-2), 1992, Figs. 2, 3, and 4.]... 

Despite this last observation, for this type of simulation and modelling research, two main means of evolution remain the first consists in enlarging the library with new and newly coded models for unit operations or apparatuses (such as the unit processes mentioned above multiphase reactors, membrane processes, etc.) the second is specified by the sophistication of the models developed for the apparatus that characterizes the unit operations. With respect to this second means, we can develop a hierarchy dividing into three levels. The first level corresponds to connectionist models of equilibrium (frequently used in the past). The second level involves the models of transport phenomena with heat and mass transfer kinetics given by approximate solutions. And finally, in the third level, the real transport phenomena the flow, heat and mass transport are correctly described. In... 

By the very nature of the profession, the chemical engineer has to deal very frequently with chemically reactive flows in various types of single-phase and multiphase reactors. Before the advent of CFD he or she typically had to use... 

As a building block for simulating more complex and practical membrane reactors, various membrane reactor models with simple geometries available from the literature have been reviewed. Four types of shell-and-tube membrane reactor models are presented packed-bed catalytic membrane reactors (a special case of which is catalytic membrane reactors), fluidized-bed catalytic membrane reactors, catalytic non-permselecdve membrane reactors with an opposing reactants geometry and catalytic non-permselective membrane multiphase reactors. Both dense and porous inorganic membranes have been considered. 

The balance of advantages and drawbacks of the monolith reactors is positive, making this reactor type very attractive for applications in multiphase processes. The modeling of monolith reactors and some concepts for reactor design are presented in Chapter 10. 

Monolith reactors have recently found applications in performing catalytic three-phase reactions (see Chapter 9). There is also growing interest in the chemical industries for this novel type of multiphase reactor. A proper modeling of the monolith reactor is a necessary step in order to estimate the overall performance of the reactor. 

Discussions on flow modeling so far have been more or less restricted to singlephase reactors. However, in a broad range of application areas, multiple phases are involved in chemical reactions (see examples cited by Ramachandran and Choudhari, 1983 Doraiswamy and Sharma, 1984 Kunii and Levenspiel, 1991 Shah, 1991 Dudukovic et al, 1999). Reactors carrying out such reactions are generically termed multiphase reactors. There are several types of multiphase reactors and several methods are available to classify these reactors. One of the simplest methods of... 

The list is merely suggestive. Complexity of reactive flows may greatly expand the list of issues on which further research is required. Another area which deserves mention here is modeling of inherently unsteady flows. Most flows in engineering equipment are unsteady (gas-liquid flow in a bubble column reactor, gas-solid flow in a riser reactor and so on). However, for most engineering purposes, all the details of these unsteady flows are not required to be known. Further work is necessary to evolve adequate representation of such flows within the CFD framework without resorting to full, unsteady simulations. This development is especially necessary to simulate inherently unsteady flows in large industrial reactors where full, unsteady simulations may require unaffordable resources (and therefore, may not be cost effective). Different reactor types and different classes of multiphase flows will have different research requirements based on current and future applications under consideration. 

Multiphase Reactors Reactions between gas-liquid, liquid-liquid, and gas-liquid-solid phases are often tested in CSTRs. Other laboratory types are suggested by the commercial units depicted in appropriate sketches in Sec. 19 and in Fig. 7-17 [Charpentier, Mass Transfer Rates in Gas-Liquid Absorbers and Reactors, in Drew et al. (eds.), Advances in Chemical Engineering, vol. 11, Academic Press, 1981]. Liquids can be reacted with gases of low solubilities in stirred vessels, with the liquid charged first and the gas fed continuously at the rate of reaction or dissolution. Some of these reactors are designed to have known interfacial areas. Most equipment for gas absorption without reaction is adaptable to absorption with reaction. The many types of equipment for liquid-liquid extraction also are adaptable to reactions of immiscible liquid phases. 

---